Microsoft's Windows 8 tablet, the Surface Pro, launches this weekend. Reviews have been mixed, with some observers dinging the paltry battery life. But a Microsoft executive has indicated the company may offer a battery add-on.

This week, Microsoft Corporate Vice President Panos Panay told an online audience via Reddit that the company may provide some accessories that could take advantage of connector plates on the device -- plates which are not found on the Surface Windows RT model. The response was to a question that asked about a possible external battery pack or keyboard/cover containing an additional battery.

The Pro has been criticized for having a battery life of 4.5 to 5 hours, about half that of other tablets. Interestingly, the Microsoft team told the Reddit audience that if the Surface Pro is compared to "a MacBook Air, you will quickly see that pound for pound in battery size versus battery life, you will find optimizations that put Surface best in its class." The MacBook Air's battery is marketed as having a life of 5 hours.

'Ultrabook-Class PC'

This Pro-to-laptop comparison appears to be a key part of Microsoft's marketing strategy of treating the device as a new category. Last week, for instance, Tami Reller, head of marketing for the company's Windows division, told news media that the $899 price for the Pro should be seen as "getting an Ultrabook-class PC with the added benefit of tablet package."

Since it first announced the Surface line last year, Microsoft has continually made the comparison to Ultrabooks, which are thin, powerful, processor-based laptops. To be compared with a laptop, however, the tablet needs the optional keyboard/cover, which goes for another $120. The MacBook Air starts at $999.

The value proposition for this device is shaping up into an assessment of whether it is a great value as a laptop-plus-tablet, or whether it accomplishes neither role well.

Tablet/PC or Neither?

On the one hand, the device has an Intel Core i5 processor, runs a full Windows 8 operating system, supports legacy Windows apps, and, with its keyboard cover, can function as a laptop. As more than one observer has noted, it's essentially a flat PC. Without the cover, it is a tablet with a kickstand and a touchscreen interface using the new Windows 8 touch interface.

On the other hand, the Surface Pro is heavier and thicker than other tablets -- 40 percent heavier than the heaviest iPad and more than 40 percent thicker. Some users have said that, under normal conditions, the battery life is actually less than four hours, problematic for a device.

Several reviewers have complained that its heft makes it clumsy to use in a lap, and that, judged against a comparable laptop, the Pro has less , fewer ports, and a keyboard/cover that does not compare. There is also no built-in cellular connectivity, which must be added through a plug-in modem.